PHILADELPHIA — City police were trying to find out who is behind an anonymous social media site that has been identifying witnesses in violent crimes across Philadelphia with the stated intention of trying to “expose rats.”

The “rats215″ account on the photo-sharing site Instagram has posted pictures, police statements and testimony identifying more than 30 witnesses since February, The Philadelphia Inquirer reported.

Police Lt. John Walker said investigators learned of the account last week when an officer monitoring Twitter spotted photos of a witness and court records from an attempted shooting last year. That led to the Instagram account where officials found witness statements from the alleged 19-year-old victim, who said he was fired upon that summer because he had testified in a homicide case, he said.

Instagram representatives said they were looking into the account, which was inaccessible by 8 p.m. Thursday, the newspaper said.

The account had nearly 7,900 followers and had been updated almost daily. It contained more than 150 photos, many drawing dozens of comments and “likes.”

“Post some new rats,” one commenter wrote in September, according to the Inquirer. “I needa put a hit out on them.”

One post praised drug dealer Kaboni Savage, who was sentenced to death for being behind a dozen murders including a firebombing that killed four children and two women.

Tasha Jamerson, a spokeswoman for the district attorney’s office, said she couldn’t comment on an investigation but called witness intimidation a “very serious, ongoing problem” that plagues Philadelphia prosecutors daily.

“We work with Philadelphia police to investigate vigorously and thoroughly any attempt to intimidate any witness, to identify perpetrators, and, where appropriate, arrest and prosecute,” she said in an email.

Veteran law enforcement officials say they have seen victims’ statements posted in barbershops, on neighborhood utility poles and even mailed to the homes of witnesses, but such statements now are as likely to wind up on Facebook, Twitter and Instagram.

Walker said investigators are now working to identify the account-holder.

“These actions shoot an arrow through the heart of the criminal justice system, placing victims and witnesses at risk,” he said.